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Cannondale’s aluminum Topstone gravel bike has proven to be quite popular since its debut last August, and the company is now following up with a higher-performance Topstone Carbon version. It’s hardly just the same frame made out of carbon fiber composite, though; it’s a totally different bike, with a radical pseudo-suspension design out back called Kingpin, heaps of tire clearance, and a generous array of accessory mounts.
Best of all, the innovative design actually works, and the new bike even looks good, too.
A primer on frame compliance
Cannondale’s new Topstone Carbon gravel bike looks radically different, and in some ways, it is. But when you really dig down into it, its clever frame design is more an extension of the comfort-enhancing principles that bicycle brands have already been using for years.
“Compliance” is the term frame designers use to describe the way frames can be made to flex over bumps to enhance rider comfort, and between the directional tunability of carbon fiber (more properly known as anisotropy) and carefully chosen tube shapes, modern high-performance frames ride far more smoothly than any round-tubed metal bike could ever hope to.
Compliance works the same way on most double-diamond bicycle frames. When hitting a bump, the rider’s cantilevered weight wants to flex the seatpost rearward and downward. Since the seatpost is rigidly connected to the seat tube, but the seat tube’s movement is limited by its connection to the seatstays and top tube, that intersection ends up effectively behaving like a pivot: as the seatpost rotates backward around that point, the seat tube wants to rotate forward, and the rest of the frame flexes a little to compensate. The whole thing wants to flex rearward and downward when the rear wheel hits something.
Metal frames and carbon frames both want to do this; it’s just that the latter is usually better at it. There are limits to compliance, however, and therein lies the brilliance of the IsoSpeed “decoupler” that Trek introduced in 2012 on the original Domane endurance road bike. Since the seat cluster wants to behave like a pivot, Trek just went ahead and put two bearings and an axle there, dramatically enhancing what the frame already wants to do, anyway.
Enter Cannondale’s new Kingpin system.
Moving the seatstays further down the seat tube is another strategy an increasing number of frame designers have been using in recent years to boost compliance. On bumps, the rider’s weight still wants to move the seatpost down and back as usual, but the seatstays now help drive the lower section of the seat tube forward, actively enhancing the flex pattern of more traditionally shaped frames.
It’s sort of like what a snowboarder does on the showroom floor when they’re trying to gauge the flex pattern of a new board: they’ll rest the tail on the ground, pull down on the nose with their hands, and use their knee to drive the middle of the board forward. In this case, the board is a seat tube, their hands are the weight on the saddle, and their knee is those dropped seatstays getting driven into the seat tube.
Much like IsoSpeed, Kingpin adds a physical pivot to remove a constraint on an already-existing flex pattern. In the case of the new Cannondale Topstone Carbon, that pivot is situated where the dropped seatstays meet the seat tube, instead of up where the seat tube meets the top tube. The other crucial elements are the kink in the seatstays down near the dropouts, the flattened chainstays, the leaf spring-like lower seat tube shaping, and — as always — some careful carbon fiber lay-up tuning that is adjusted according to frame size in an effort to provide every Topstone rider with the same ride experience.
Taken in total, Cannondale claims up to 30mm of movement, with roughly 75% of that happening up at the saddle (where it’s needed most) and the rest down at the rear axle. Put another way, Cannondale says Kingpin is akin to increasing tire width by 9mm — and given what we know about how much tires affect ride quality, that’s a bold claim. But much like the effectiveness of IsoSpeed is immediately obvious when you push down on the saddle in a shop, you can very obviously see the Topstone Carbon’s seat tube flexing as intended, too.
Once you see the frame moving for yourself (or ride it!), those claims suddenly seem a little less outlandish.
Torsional and bottom bracket stiffness are maintained through the use of a large-diameter down tube that’s especially fat up by the tapered head tube, a notably wide seat tube, and broad chainstays, all of which make full use of the real estate provided by the 83mm-wide bottom bracket shell.
Kingpin doesn’t seem to add much weight, either. Claimed weight for a painted medium-sized frame is a reasonable 1,305g, including hardware, plus another 480g for the matching full-carbon fork.
Cushiness everywhere, an abundance of accessory mounts
Trek’s early IsoSpeed-equipped bikes were often criticized (including by me) for offering a smooth ride out back, but a comparatively harsh ride up front. Trek eventually added a similar mechanism up front, but Cannondale is hoping to avoid similar criticisms here right out of the gate.
Cannondale benefits from timing here, not to mention the rise of the gravel category. Where the first-generation Domane came with 28mm tires that were intended to be used mostly on tarmac, the Topstone Carbon is a gravel bike that comes with far more forgiving 700x37mm tires. If you want even more of an air cushion below you, Cannondale says the Topstone Carbon frame and fork will accept tires up to 700x40mm or 650x48mm. That’s with a minimum of 6mm of clearance all around, too, so riders that are a little less risk-averse will likely be able to squeeze slightly wider rubber in there.
To help balance out the softer feel of the Kingpin rear end, the top-end model is fitted with the SystemBar integrated cockpit that Cannondale had originally hoped to roll out with the new Synapse last year. The way the carbon bar bolts directly to the aluminum stem looks slick, sure, but it’s the dramatically flattened bar tops that presumably provide more tangible benefit when the terrain gets rowdy. According to Cannondale, the SystemBar is good for 4-6mm of movement during regular riding (with up to 15mm of movement seen in lab tests). Other models are equipped with conventional cockpits, though.
Regardless of model, more flex is offered out back by the standard round 27.2mm-diameter SAVE carbon seatpost, which is carved-out up top to help promote more movement under load.
Cannondale hasn’t skimped on accessory mounts here, which makes sense given the Topstone’s obvious versatility. There are fittings for three bottle cages (with one under the down tube), mounts for both a lowrider rack and fender up front, rear fender mounts, and a place on the top tube for a feed bag, too.
Cable routing is internal through the down tube with fully guided paths from end to end; just insert the housing or hose at the head tube, and it magically pops out down by the bottom bracket. There are also accommodations for a dropper seatpost should you want one, and the 12mm front and rear thru-axles utilize Mavic’s SpeedRelease system. This theoretically makes for faster wheel changes, but the more practical benefit is arguably the fact that there’s less of a chance of inadvertently leaving an axle behind since you now no longer have to remove it completely from the hub in order to remove or install a wheel.
As is currently fashionable, the seatpost is fixed in place with an internal wedge system similar to what Cannondale uses currently on the F-Si hardtail.
There’s also a custom wireless speed sensor included on higher-end Topstone Carbons that neatly attaches to the front hub and was developed in partnership with Garmin. It functions the same as any other wheel sensor if you wish, connecting with various head units via common ANT+ or Bluetooth LE protocols. But it’s also designed to work with Cannondale’s own smartphone app should you prefer a more unobtrusive way to record your rides (GPS location is dependent on the phone). The app also provides maintenance reminders based on actual usage.
Cannondale is offering the Topstone Carbon in five sizes: XS (48cm), S (51cm), M (55cm), L (58cm), and XL (61cm). All feature moderately upright rider positioning with linear stack and reach progression as you move through the size range, and the identical stack and reach dimensions as the current Topstone.
Geometry on the new Topstone Carbon is mostly shared with the Topstone, with the same 55mm fork rakes, but very subtly steeper head tube angles that make for slightly reduced trail dimensions and modestly quicker front-end handling as a result. Interestingly, though, Cannondale has raised the bottom bracket on the Topstone Carbon significantly. Whereas the aluminum Topstone boasts 75mm of bottom bracket drop across the board, each Topstone Carbon’s bottom bracket sits at 59-69mm below the hub axles, depending on size.
Presumably, this was done to prevent pedal strikes if a Topstone Carbon is set up with 650b wheels and tires — a strategy I’ve seen an increasing number of brands utilize — but as is always the case with this sort of thing, it’s a compromise that not everyone will agree with.
Another major change is out back. Where the aluminum Topstone uses 430mm-long chainstays, the Topstone Carbon tightens that figure to a comparatively stubby 415mm for more responsive handling and a more road bike-like feel — particularly impressive given the tire clearances and the fact the bike is still designed around a two-chainring drivetrain.
Overall, riders sampling both Topstone versions back to back will likely find the aluminum version to lean a bit more toward the stability end of the spectrum, while the Topstone Carbon is intended to feel a bit more nimble.
Paying the piper
At this point, you may be wondering how exactly Cannondale managed to provide generous tire clearance, two-ring drivetrain compatibility, and such short chainstays. As always, you don’t get something for nothing.
The Topstone Carbon uses Cannondale’s BB30-83 Ai bottom bracket shell, which is similar to standard BB30 in that the bearings press directly into the frame. Already used on the Synapse, SuperX, and F-Si hardtail, BB30-83 Ai is an asymmetrical shell that’s 5mm wider on the non-driveside than than driveside, and 83mm-wide overall. According to Cannondale, this provides more space for the chainstays to move outward for increased tire clearance.
Also borrowed from the F-Si and SuperX is Cannondale’s Ai, or asymmetric integration, concept. This offsets the entire drivetrain outward by 6mm, which creates even more room for tires and drivetrain bits.
Downsides? Well, the wider bottom bracket shell requires a longer spindle, which then increases the Q-factor relative to standard road bikes. Granted, narrower Q-factors aren’t universally better for everyone, but nevertheless, many riders will likely be bummed to see this.
And while the rear end uses standard 142mm-wide hubs, the rim has to be dished over to the non-driveside to keep it centered in the frame. This actually improves wheel strength by evening out the spoke bracing angles, but it also means that off-the-shelf wheels won’t work without modification (which won’t always be possible). And then there are all the proprietary parts required, such as the custom bottom bracket spindle and custom chainring spider.
Consider it the price of progress, I guess.
Models, availability, and pricing
Cannondale is offering the Topstone Carbon in up to five complete builds, depending on region. All models use identical framesets, 700c wheel-and-tire setups, and two-chainring drivetrains. Prices start at US$2,700 / £2,100 / €2,600 for the Topstone Carbon 105, and top out at US$6,500 / AU$7,500 / £4,800 / €5,500 for the Topstone Carbon Force eTap. Unfortunately for DIYers, there are currently no plans to offer a separate frameset – and Australia will only get the flagship model and the mid-range Topstone Carbon Ultegra RX2.
Continuing a most-welcome recent industry trend, though, all of the new Topstone Carbon models should at least otherwise be available at retailers immediately.
Actual weight for the flagship model in a medium size is 8.75kg (19.29lb), without pedals.
Riding the Topstone Carbon
Cannondale invited editors to sample the new Topstone Carbon at the resort area of Stowe, Vermont, an area replete with lush green rolling hills, winter-ravaged tarmac, hidden singletrack, and a seemingly endless array of unpaved roads — in other words, ideal grounds for a bike intended for mixed terrain. Cannondale provided a Topstone Carbon Force eTap at the event, but also shipped me a Topstone Carbon Ultegra RX in the weeks leading up to the launch event, so I thankfully was able to sample the new chassis on more familiar terrain as well.
The Kingpin suspension design is clearly effective, not only taking the edge off bigger hits, but also smoothing out mellower terrain. In general, it offers a noticeably smooth, comfortable, and composed ride that’s well suited to the bike’s go-anywhere, do-anything mission.
It’s not without its quirks, though. Cannondale equips each Topstone with 700x37mm WTB Riddler tires, which I normally run at about 32-34psi, depending on terrain. At those pressures, Kingpin honestly doesn’t seem to do a whole lot; the tires are doing all the work of absorbing the bumps. But when I increased the pressure to around 36-38psi, Kingpin started to kick in, offering a similarly cushy ride as before, but with a faster roll on harder surfaces and a more supportive feel down at the tire contact patches.
I’d normally be averse to being forced to run a higher pressure than I really want, but I was OK with it in this case. Higher-end Topstone Carbon models are fitted with Cannondale new Hologram HG22 carbon clincher wheels, and their 25mm inner width flattens out the profile of the Riddler more than WTB’s designers originally intended. At that lower air pressure (I’m about 70kg, by the way), those Riddlers feel dull and slow, since the chunky side knobs that normally only come into play in corners now rumble along the ground when going straight, too. But at the higher pressure, the tire rides more on the crown as it’s meant to.
The SystemBar seems to work as intended, as the Topstone Carbon I rode in Vermont delivered a reasonably balanced ride quality front-to-back, particularly in group situations on the road where we were regularly smacking into nasty, wheel-swallowing potholes with minimal warning.
The test sample I have at home is equipped with a conventional aluminum bar and stem, however, and as I feared, it highlights the fact that the front end of the Topstone Carbon frame and fork isn’t nearly as compliant as the rear end with the Kingpin system. The high-volume tires obviously help a ton, but once you’ve exhausted whatever cushioning is on tap there, the frame doesn’t seem to have anything left to offer. While I ended up running both tires on the SystemBar-equipped Topstone Carbon Force eTap at similarly higher pressures, I ended up running a lower pressure up front on the Topstone Carbon Ultegra RX I’ve got at home.
As promised, though, torsional and bottom bracket frame stiffness are excellent, with a snappy feel when climbing out of the saddle or sprinting, and a generally reactive personality that should satisfy most riders coming straight off traditional road bikes. The chassis is stout and solid under power, and there seem to be no downsides to the additional hardware out back.
Some might lament the subtly sped-up handling on the Topstone Carbon relative to the aluminum Topstone (and many other gravel bikes, for that matter), but I actually prefer it for its more sporting feel. The bike is still pretty stable overall, but there’s a degree of quickness when you want it that I sometimes find lacking in the category.
How much of a difference does that 15mm reduction in chainstay length really make? Well, I generally find bikes that are that long out back to feel a bit like you’re towing a semi trailer. But at least to me, the Topstone Carbon feels a little more flickable and responsive, and yes, a bit more road bike-like in that respect.
At least for now, initial impressions are promising, but a few questions linger in my mind. How much will that noticeably wider Q-factor bother me over the long term, if at all? And what about all those proprietary bits and the disparate front-vs.-rear ride quality? Stay tuned for a proper long-term review in the weeks ahead.